Hey guys, I know a lot of you have, in the past, wanted that Holley 3739 TBI unit from back in the day (which is basically unobtainium). Well... I recently picked up a 1984 Chevrolet Corvette, which has Cross-Fire Injection on a 350 V8. I remember from back in the day, that my 82 TransAm (which also had at one point CFI), had the same TBI units. I was looking for some performance options for the Cross Fire Injection (since I find that system to be so unique) and ran across this company called, X-Fire Performance.
They provide a boring service for the Cross-Fire Injection throttle bodies, which happen to be the exact same TBI unit that's on our 1984-1986 Pontiac Fiero. They offer the service for $900, but that's for TWO of them (since the 82-84 Corvettes have two of these throttle bodies in the Cross-Fire Injection system). I just mentioned this to the owner, and he said he'd be happy to offer the service for 4 cyl Fiero owners.
If you've been looking for one of those aftermarket Holley 3739 performance TBI units... you don't need to spend $1,000 anymore, because you can get one bored (larger) for less than half that. Feel free to reach out to them via their contact form.
I didn't know. Have not gone to thirdgen.org in ages. It is one of the more knowledgeable tuning sites. Bob helped many people out even if they didn't buy his own product. Rip Bob
If the modified TBI unit accepts the Fiero injector it will make the tuning job much easier. Editor Programs are available that will allow changes to the fueling table in the ECM but it may not be needed. Run with it, monitor the O2 sensor with a scanner and see.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
If the modified TBI unit accepts the Fiero injector it will make the tuning job much easier. Editor Programs are available that will allow changes to the fueling table in the ECM but it may not be needed. Run with it, monitor the O2 sensor with a scanner and see.
It does! You send them just the base plate (they don't do anything with the fuel metering part) and they send it back to you restored and bored out. You can send them the top part (if you want it refinished like the bottom part), but that's an extra charge. There are also aftermarket injectors that will fit this TBI unit in stock of the factory injector (if you prefer).
Originally posted by 82-T/A [At Work]: It does! You send them just the base plate (they don't do anything with the fuel metering part) and they send it back to you restored and bored out. You can send them the top part (if you want it refinished like the bottom part), but that's an extra charge. There are also aftermarket injectors that will fit this TBI unit in stock of the factory injector (if you prefer).
I was alluding to correct injector flow but it looks like you have that solved. THis TB conversion may be exactly what Duke Fiero owners are looking for especially if a turbo is added. With a cam, 5 psi of boost and some port work, a 135HP Duke is possible and would make life easier for some.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Ok, so... my daughter and I got the car back together and we drove it around for what seemed like an hour. I put about 40 miles on it.
We installed a K&N air filter. The factory K&N air filter is no longer available, but I made one by cutting up a similar height one that has a larger diameter. Worked perfectly. We also installed a hotter ignition coil from Summit Racing. It's only a modest upgrade over the stock coil, and puts out 35,000 volts, which is a bit higher than the stock coil which is usually anywhere from 25-30k volts. We also installed a new fuel filter from K&N (really, just a quality replacement), but also installed the 50mm bored out intake manifold and the 46mm bored throttle body unit.
The only real big issue I ran into was that... God knows why... I forgot to install the gasket between the two halves of the top of the TBI unit. Both my daughter and I have rebuilt a dozen of these... and for some reason I forgot. I wonder if it maybe slipped off when I was installing it. It's all I can think of. Anyway, we turned the key, got fuel pressure and it cascaded fuel all over the top of the engine. It dulled the paint on the valve cover, which bummed me out... but we got it cleaned out, let it dry out, and then put the gasket back on.
Once we got it started, it was a little rough, but after a couple of minutes, it was running perfect. We burped the coolant a few times, and then drove around for 10 minutes. It ran quite well... no smoke, nothing. I let it cool off, put a few more things back together, and then drove it around for like almost an hour, and we took it through several sweeping backroads.
The front suspension is totally shot, and the doors don't have bump stops on them so they bang when you hit a bump, but other than that... the rest of the car is totally restored, and the engine sounded AMAZING... I mean, really, really amazing. It doesn't at all sound like a typical clattery Iron Duke.
Next weekend, we're going to hook up Paul Romsky's ALDL ECM reader and check the AFR to see how it's behaving. Per CarterCarb's recommendations, I haven't been driving it hard. Never more than 3k rpms at the absolute most... mostly shifting at 2,000 rpms. But there's lots of power, and I can absolutely tell a difference. I think it's running a little rich based on smell, but man, the car runs so well and everything is SUPER smooth...
Ok, so... my daughter and I got the car back together and we drove it around for what seemed like an hour. I put about 40 miles on it.
We installed a K&N air filter. The factory K&N air filter is no longer available, but I made one by cutting up a similar height one that has a larger diameter. Worked perfectly. We also installed a hotter ignition coil from Summit Racing. It's only a modest upgrade over the stock coil, and puts out 35,000 volts, which is a bit higher than the stock coil which is usually anywhere from 25-30k volts. We also installed a new fuel filter from K&N (really, just a quality replacement), but also installed the 50mm bored out intake manifold and the 46mm bored throttle body unit.
The only real big issue I ran into was that... God knows why... I forgot to install the gasket between the two halves of the top of the TBI unit. Both my daughter and I have rebuilt a dozen of these... and for some reason I forgot. I wonder if it maybe slipped off when I was installing it. It's all I can think of. Anyway, we turned the key, got fuel pressure and it cascaded fuel all over the top of the engine. It dulled the paint on the valve cover, which bummed me out... but we got it cleaned out, let it dry out, and then put the gasket back on.
Once we got it started, it was a little rough, but after a couple of minutes, it was running perfect. We burped the coolant a few times, and then drove around for 10 minutes. It ran quite well... no smoke, nothing. I let it cool off, put a few more things back together, and then drove it around for like almost an hour, and we took it through several sweeping backroads.
The front suspension is totally shot, and the doors don't have bump stops on them so they bang when you hit a bump, but other than that... the rest of the car is totally restored, and the engine sounded AMAZING... I mean, really, really amazing. It doesn't at all sound like a typical clattery Iron Duke.
Next weekend, we're going to hook up Paul Romsky's ALDL ECM reader and check the AFR to see how it's behaving. Per CarterCarb's recommendations, I haven't been driving it hard. Never more than 3k rpms at the absolute most... mostly shifting at 2,000 rpms. But there's lots of power, and I can absolutely tell a difference. I think it's running a little rich based on smell, but man, the car runs so well and everything is SUPER smooth...
get her broke in and then hammer it. the engine that head came off had no shortage of power and definitely spun up to 6500 a few times (stupid automatic.) but it should beat out a stock v6 manual pretty easy.
It's definitely not like my 85 GT 4-Speed that I bought from Darrell Morse... it had the heads decked (higher compression), and he'd swapped in a 4.10:1 4-Speed. It was crazy.
But this Iron Duke my daughter has... I am SUPER impressed with how it drives. I'm not going to make claims about beating V6s, but Patrick... I'm barely accelerating and it pulls quick. It feels like my Solstice GXP 5-Speed when it's not currently getting boost (like anything under 3,500 rpms).
I can tell it's running a little rich, so we're going to fix that, but otherwise I am sooo incredibly impressed.
I did the thing you mentioned (stuffing wire mesh into the baffle), and I dunno... maybe that made a difference? When I'm behind the engine with the decklid up, I don't hear the typical "clackety" sound I normally hear from a Duke.
I'm barely accelerating and it pulls quick. It's really, really smooth.
Todd, I love the fact that this duke is smooth, and pulls quick... but it's not, I repeat, it's not going to beat a 2.8 (especially one with a manual) that's running properly. I have several Fieros, including an '84 duke (with a swapped in 5-spd) which runs great... but there's not a chance that it would give my Formula a run for its money. I've autocrossed both cars. The Formula is much quicker, it's not even close.
[This message has been edited by Patrick (edited 11-23-2025).]
Todd, I love the fact that this duke is smooth, and pulls quick... but it's not, I repeat, it's not going to beat a 2.8 (especially one with a manual) that's running properly. I have several Fieros, including an '84 duke (with a swapped in 5-spd) which runs great... but there's not a chance that it would give my Formula a run for its money. I've autocrossed both cars. The Formula is much quicker, it's not even close.
Hahah... I know... but I do wonder what kind of power it's putting out. I'm not really sure... but if I had to pull a number out of my head... maybe ~110-120? It's so different than any other Duke I've owned.
This car still needs a bunch of stuff. Front suspension, doors, steering column (stalk, horn, ignition), and then some finishing details. We're getting close... but still needs more.
A while ago Pfaff Turbo and High Tech Turbo made Turbocharger kits for the Fiero Duke Engines. They advertised that the kits with 5 psi of boost made 135 Horsepower. With the popularity of the 2.8L V6 increasing the kits became obsolete. The other thing that killed the kits was that after they were installed some owners loved the extra power and adjusted the wastegate to provide higher boost. The Duke engines did not react well and with more than 5 psi of boost they failed. Point is that these engines can take only LOW boost.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 11-24-2025).]
A while ago Pfaff Turbo and High Tech Turbo made Turbocharger kits for the Fiero Duke Engines. They advertised that the kits with 5 psi of boost made 135 Horsepower. With the popularity of the 2.8L V6 increasing the kits became obsolete. The other thing that killed the kits was that after they were installed some owners loved the extra power and adjusted the wastegate to provide higher boost. The Duke engines did not react well and with more than 5 psi of boost they failed. Point is that these engines can take only LOW boost.
My experience with turbos is that they generally need higher RPM to perform well... unless it's just been my exposure to them. I know that turbo diesels don't at all have higher revving engines. I suppose it's a function of the design of the turbo. 135hp is not bad, but in my opinion introduces a lot of complexity to an otherwise simple and reliable motor. I'm debating a turbo... but not on this car. I may want to buy a more modern coupe and swap in a turbo into that.
Ok, we put another 40 miles on the car today after I was done with work. It runs really nice... but I went through almost a quarter of a tank. I'm getting a puff of white smoke when it's sitting. Not when I'm driving around, but if I let it idle for any extended period of time, and then blip the gas, I get a puff of white smoke.
I just did a ton of research because I was concerned about it possibly being something with the cooling system... but definitely not that. I'm not losing any coolant, and everything is buttoned up. I found several sites that said the white smoke is unburned fuel... which would make sense. "Unburned fuel turns into white smoke, which you will see coming out of the exhaust." I'd actually never heard of this, but did several searches and confirmed it.
I did a wild ass guess when I adjusted the fuel pressure regulator as I was rebuilding the TBI unit and using the adjustable fuel pressure regulator from the Corvette throttle body... so, our next task is to use the ALDL scanner that Paul Romsky built, so I can at least adjust the FPR to a level where it's normal.
We only put like 40 miles on it today, and I burned almost a quarter of a tank of gas... and it was almost all casual driving at 2,000 rpms around 35-50 miles an hour. No flooring it, and no crazy acceleration. Makes me feel a little bit better since I was starting to get concerned again (it's running amazing). It will be nice once I have the FPR adjusted and appropriately configured to match the increased bore.
I found several sites that said the white smoke is unburned fuel... which would make sense. "Unburned fuel turns into white smoke, which you will see coming out of the exhaust." I'd actually never heard of this, but did several searches and confirmed it.
To me, that doesn't make sense. Where exactly did you read that?
White smoke is water/condensation Blue smoke is oil Black smoke is excess fuel
Most websites just assume / always that it's a blown head gasket... but I'm not having any issues at all like that. I do know it's running really, really rich though.
I'm willing to bet that the reported "white smoke, fuel dripping from tail pipe" was simply condensation/water. There's no way that was "fuel" dripping out of his tailpipe.
get her broke in and then hammer it. the engine that head came off had no shortage of power and definitely spun up to 6500 a few times (stupid automatic.) but it should beat out a stock v6 manual pretty easy.
which head is this if I might ask? It's not the SD4 head is it?
I'm willing to bet that the reported "white smoke, fuel dripping from tail pipe" was simply condensation/water. There's no way that was "fuel" dripping out of his tailpipe.
I'm not getting any fluid like that out of the tailpipe, I did get a couple of drips when I first started it (which I'm sure is condensation). The car hadn't run in like 3 months. But what I'm getting is a cloud of smoke only after the car has been sitting. The fuel pressure regulator is off, and the injector is a much larger injector too... and I'm guessing that fuel is pooling in the intake manifold while it's sitting at idle. Then when I blip the throttle, it takes all of that excess fuel at once and it's just too much... and creates that cloud of smoke.
But driving around, not a single bit of smoke anywhere. Runs well, I'm just getting horrible fuel economy. And then when I pull into a spot and let the car sit for more than a couple of minutes, and blip the throttle... a little cloud of smoke.
I plan to lean it out... but there's an adjustment tool that I really want to get... otherwise, I have to keep taking the top of the throttle body off.
This sneaks right up and under the fuel pressure regulator (little hole in the bottom of the bowl) and allows you to turn the bolt to raise and lower the spring pressure plate. I assume the tighter the spring (in the FPR) the less fuel will come out of the injector?
quote
Originally posted by ironpuke84:
which head is this if I might ask? It's not the SD4 head is it?
It's not the SD4 head, but it's also not a stock Fiero head. The Fiero heads all have the year stamped in them, and the casting is a bit more open (for oil to drain down). I can't remember the website, but it talked about several cyl heads that were ever so slightly better than the stock Fiero head, and were recommended for using if you were building a performance duke. I don't remember what engines they came from... maybe the S10? That wasn't my goal, but I ran the head casting number, and it ended up being one of the ones it recommended (if you couldn't find or afford an SD4 head). To me personally, I can't tell a bit of difference between a stock Fiero cyl head and this cyl head. It seems to have a little bit more meat in some places, but supposedly it has slightly larger intake passages with some restriction removed. I hadn't really paid much attention to that, and was just more interested in getting it installed.
But it runs pretty nice... lots of low-end torque. I haven't been flooring it at all, but it effortlessly pulls off the line below 3,000 rpms.
EDIT: I looked it up... it ended up being a 552 cyl head. From another forum, it said: "The exhaust ports aren’t really any better, but the intake ports are better and the intake valves aren’t shrouded like they are in the 1984-1986 767 casting heads."
[This message has been edited by 82-T/A [At Work] (edited 11-25-2025).]
Originally posted by 82-T/A [At Work]: It's not the SD4 head, but it's also not a stock Fiero head. The Fiero heads all have the year stamped in them, and the casting is a bit more open (for oil to drain down). I can't remember the website, but it talked about several cyl heads that were ever so slightly better than the stock Fiero head, and were recommended for using if you were building a performance duke. I don't remember what engines they came from... maybe the S10? That wasn't my goal, but I ran the head casting number, and it ended up being one of the ones it recommended (if you couldn't find or afford an SD4 head). To me personally, I can't tell a bit of difference between a stock Fiero cyl head and this cyl head. It seems to have a little bit more meat in some places, but supposedly it has slightly larger intake passages with some restriction removed. I hadn't really paid much attention to that, and was just more interested in getting it installed.
But it runs pretty nice... lots of low-end torque. I haven't been flooring it at all, but it effortlessly pulls off the line below 3,000 rpms.
EDIT: I looked it up... it ended up being a 552 cyl head. From another forum, it said: "The exhaust ports aren’t really any better, but the intake ports are better and the intake valves aren’t shrouded like they are in the 1984-1986 767 casting heads."
This looks very promising, I look forward to seeing how it performs under wide open throttle. Hopefully if this works well many 2.5L owners like myself will get a bit more kick out of the old Duke.
This looks very promising, I look forward to seeing how it performs under wide open throttle. Hopefully if this works well many 2.5L owners like myself will get a bit more kick out of the old Duke.
I think the biggest thing is making sure that the intake manifold is properly matched to the bored TBI unit. From what I can tell so far, the car feels lighter, if that makes sense... it feels like there's less effort to get the car moving and to accelerate (compared to a few months ago with the stock TBI unit).
The problem... not so much a problem as a difficulty, is that she's upgraded a lot of things on the car. It has the 88 accessories, a lighter alternator with less rotating mass, a decoupler pulley, a shorty header, bored intake and bored throttle body, a supposedly better cyl head, a harmonic balancer, a rebuilt transmission with better gearing, and a newer catalytic converter. So, while it does all add-up, it's hard to tell what made the biggest difference.
But it would be great once it's broken in, to get it dynoed to see what all these things add up to.
My guess is that I'm probably seeing around ~115hp, maybe 120hp with everything.
We got a laptop set up and installed Paul Romsky's ALDL scanner / reader. Unfortunately, the laptop can't hold a charge (ordered a new battery), so in the mean time, we ran it idling / warm in the garage. I've recently had a problem (since we re-installed the cyl head), that the temperature gauge on the dash is not showing temperature at all. Like... AT ALL. The needle is firmly planted at the 100 mark, and just sits there. It full warms up, and I can show with my temperature gun that it's getting to 180-190 at the filler neck, and around ~200-210 at the cyl head.
So, I hooked up Paul's ALDL reader and loaded up the scanner GUI, and oddly enough, his temperature gauge (which is reading from the CTS) also shows that it's extremely cold (I think it said something like 50 degrees or whatever). So both my actual gauge, and his CTS-read gauge are not reading temperature... of course, I don't think it's a problem with his scanner... it actually makes me realize that either my engine is running below 100 degrees (I kind of doubt it), or it's sharing a ground wire that's not properly grounding.
We must have forgotten a ground somewhere... so I'm going to go back and look in there. It's pretty cool though...
But it would make sense why the fuel economy is soooo bad. It's thinking the engine is running at extremely cold temperatures so it must be dumping a ton of fuel in there.
